Quote taken from the report:
“Another sensitive issue raised in the report was the risk of brain cancer from cell phones. Scientists are divided on whether there is a link. Until more research is conducted, the panel recommended that people reduce their usage by making fewer and shorter calls, using hands-free devices so that the phone is not against the head and refraining from keeping a phone on a belt or in a pocket. Even if cell phones raise the risk of cancer slightly, so many people are exposed that “it could be a large public health burden,” Schettler said”

Link to full report: http://deainfo.nci.nih.gov/advisory/pcp/pcp08-09rpt/PCP_Report_08-09_508.pdf